Gualda's team studied deposits in the Long Valley Caldera in northeastern California, where a violent eruption blew 150 cubic miles of molten rock into the atmosphere, blanketing much of North America with hot ash and dropping the earth's surface more than a mile as it sank into the area once occupied by the magma. That was about 760,000 years ago, but all these years later the region still keeps a lot of scientists on the edge of their seats.
The Long Valley geology began misbehaving again in 1978 when a 5.4 earthquake struck six miles southeast of the caldera, suggesting that the volcano might be reasserting itself. In subsequent years that was followed by swarms of small quakes, which are closely associated with pending volcanic eruptions.
A couple of decades ago, trees began dying on nearby Mammoth Mountain from large amounts of carbon dioxide seeping from the magma, according to the U.S. Geological Survey.
Today, the caldera seems to be quieting down, despite several recent bursts of seismic events, but it is probably the most closely watched volcano on the planet. Scientists with the USGS are keeping a close eye on it, monitoring every little belch, and they insist there is no reason for the folks who live in California to be concerned. At least not yet.
Meanwhile, scientists at Oregon State University have been focusing their attention on Yellowstone National Park, where an eruption a couple of million years ago is believed to have been 2,000 times larger than Mount St. Helens. That region also shows constant signs of seismic unrest, and there have been eruptions there several times in the past, according to the Oregon researchers.
Incidentally, researchers at Washington State University in Pullman, who have also been studying Yellowstone, concluded earlier this year that the big eruption 2 million years ago wasn't one blast, but two, separated by about 6,000 years.
But just because it was split into two parts doesn't mean it was benign. The Washington researchers believe the first blast was the biggest, and it darkened the sky with ash from California to the Mississippi River.
So super-volcanoes cannot be ignored, and now it seems they can pull the trigger much more quickly than anyone had thought.